1. Field of the Invention
The present invention relates to an immersion-type substrate processing apparatus for processing a thin plate substrate such as a semiconductor substrate and a glass substrate for a photomask (hereinafter simply "substrate"). The present invention also relates to a method of controlling flows of a processing fluid in a processing bath wherein a substrate is immersed.
2. Description of the Background Art
FIG. 23 is a vertical cross sectional view showing major portions of a conventional immersion-type substrate processing apparatus.
A processing bath 1 is filled with a processing fluid 2 such as a cleaning fluid and a chemical fluid (hereinafter simply "processing fluid"). Lower rims of substrates 3 are inserted into guide grooves 7a of three substrate holding poles 7 which extend in a direction perpendicular to the plane of FIG. 23, resulting in that the substrates 3 are held upright by the substrate holding poles 7. Held by the substrate holding poles 7, the substrates 3 are immersed into the processing fluid 2, whereby predetermined treatments for surfaces of the substrates 3 are performed.
Processing fluid supply pipes 4 are disposed below the substrates 3 in the processing bath 1. The processing fluid supply pipes 4 penetrate the processing bath 1 outside at side walls of the processing bath 1 in a direction perpendicular to the plane of FIG. 23, and are fixed liquid-tight at through holes of the processing bath 1.
The processing fluid supply pipes 4 are single-layer pipes. On a side surface of each processing fluid supply pipe 4, a plurality of fluid outlet holes 5 are formed in a line at predetermined intervals in a direction perpendicular to the plane of FIG. 23 toward approximate centers of the substrates 3. A predetermined processing fluid 2 is supplied to the fluid supply pipes 4 from a processing fluid supply apparatus (not shown) which is disposed external to the processing bath 1. The processing fluid 2 is gushed out from the outlet holes 5 toward the substrates 3.
Jet flows of the processing fluid 2 sweep upward over the surfaces of the substrates 3 and the processing fluid 2 flows over a brim 1a of the processing bath 1 to be collected by an external bath 6 which is externally attached to the periphery of the processing bath 1. The processing fluid 2 thus collected is then drained through a drain pipe 6a.
In this manner, the surfaces of the substrates 3 are processed in the processing bath 1 with the processing fluid 2 which rushes from below toward upward and flows over the brim of the processing bath (Overflow method). Since there is always a fresh supply of the processing fluid 2, the processing time is short.
Nevertheless, the overflow method as above has a limited success in supplying a processing fluid to an immersion-type substrate processing apparatus. That is, some of the processing fluid 2 which is supplied through the processing fluid supply pipes 4 into the processing bath 1 stagnates in some particular area. Inconveniently enough, there is no new supply of the processing fluid 2 to this particular area (The a particular area where the processing fluid 2 stagnates will be hereinafter referred to as the "stagnant zone.").
FIG. 24 is a diagram showing flows of the processing fluid 2 across a central cross section of the processing bath 1.
Jet flows of the processing fluid 2 from the outlet holes 5 of the right side and the left side processing fluid supply pipes 4 collide each other in the vicinity of the center of the substrate 3 and deviate from each other toward the right and the left sides. Some jet flows flow outside over the brim 1a and other jet flows turn downward along the inner side walls of the processing bath 1. The latter jet flows of the processing fluid 2 then start circulating in the bath and eventually flow outside over the brim 1a.
Some of the flows of the processing fluid 2 returning to the bottom of the processing bath 1 remain circulating slowly halfway between the right side and the left side processing fluid supply pipes 4 as stagnant eddies 2a and 2b. Since there is not much supply of the processing fluid 2 directly to these areas, the stagnant eddies 2a and 2b become a stagnant zone A.
No matter how much processing fluid 2 is supplied from the processing fluid supply pipes 4, there will be almost no new supply of the processing fluid 2 to the stagnant zone A. This causes the processing fluid 2 to remain circulating the same area. Therefore, if particles or extraneous materials such as heavy metal created during surface processing of the substrates 3 (hereinafter simply "extraneous materials") are caught in the stagnant zone A, the extraneous materials will not be carried by jet flows outside the processing bath 1 over the brim 1a. Instead, the extraneous materials will stay in the stagnant zone A forever.
The extraneous materials trapped in the stagnant zone A tend to adhere to the surface of the substrate 3, thereby deteriorating the processing of the substrate.
There is another problem with this conventional method. The amount of the processing fluid 2 ejected from the outlet holes 5 is sometimes different between the right side and the left side processing fluid supply pipes 4. If this difference becomes large, other stagnant zone will be created in other region, again causing the problem as above.